1. Technical Field
The present invention relates to a technology which enables reducing defects occurring when images are displayed on liquid crystal panels.
2. Related Art
Liquid crystal panels are each configured to include liquid crystals interposed between a pair of substrates the distance between which is kept constant.
More specifically, such a liquid crystal panel is configured to include a pair of substrates, one having pixel electrodes for respective pixels therein, which are arrayed in a matrix shape, the other one having a common electrode therein, which is provided so as to be common across the pixels, and liquid crystals interposed between the pixel electrodes and the common electrode. When a voltage of a level in accordance with a gray scale is applied and maintained between each of the pixel electrodes and the common electrode, alignment conditions of the liquid crystals interposed therebetween are determined for each pixel corresponding to the pixel electrode, and thereby, a transmittance ratio or a reflection ratio of each pixel is controlled. Therefore, it can be said that, in such a configuration as described above, among electric fields acting across liquid crystal molecules, only components of the electric fields, which extend in a direction from the pixel electrodes towards the common electrode (or in a direction opposite thereto), that is, in a direction vertical to (in a direction longitudinal to) the surfaces of the substrates, contribute to display controls.
By the way, owing to a recent trend, in which pitches between adjacent pixels have become smaller in response to demands for downsizing liquid crystal panels and increasing high-resolution displaying capability thereof, electric fields are likely to occur between adjacent pixel electrodes, that is, electric fields are likely to occur in a direction parallel to the surfaces of the substrates, and influences thereof have been increased to an unignorable extent. For example, owing to the influences, there has occurred a problem in that, in liquid crystal panels employing a method, such as the twisted nematic (TN) method and the vertical alignment (VA) method, once lateral-direction electric fields are applied to liquid crystal modules, which are to be driven by longitudinal-direction electric fields, areas where alignment failures of liquid crystal molecules occur (the areas are called reverse tilt domains), and thus, lead to defects in displaying of images.
In order to reduce the influences due to the reverse tilt domain, various technologies, such as a first technology, in which the structure of a liquid crystal panel is improved by determining the shape of a light shielding layer (an aperture portion) in accordance with the positions of pixel electrodes (for example, refer to JP-A-6-34965 (FIG. 1)), and a second technology, in which, it is determined that the reverse tilt domains occur in the case where an average luminance value calculated from video signals is smaller than or equal to a threshold value, and video signals each having an output signal value larger than or equal to a preset output signal value are clipped (for example, refer to JP-A-2009-69608 (FIG. 2)), have been proposed.
However, there are disadvantages in that, the above-described first technology, in which the occurrences of the reverse tilt domains are reduced by improving the structure of liquid crystal panels, is likely to decrease an aperture ratio, and further, cannot be applied to liquid crystal panels which have already been manufactured without performing the improvement of the structure thereof. Furthermore, there is a disadvantage in that, in the above-described second technology, in which video signals each having an output signal value larger than or equal to a preset output signal value are clipped, the brightness of displaying images is limited to the preset output signal value.